Retroreflective sheeting containing a validation image and methods of making the same

ABSTRACT

This invention relates to retroreflective sheeting which has an image, such as an image. More specifically, the image has varying appearance at different angles of view. The retroreflective sheeting has a layer of transparent microsphere lenses, a transparent polymeric spacing layer underlying, contacting, and conforming to the bottom of the lenses, the spacing and conformation of which is critical to the optimal performance of the retroreflective article, a reflective layer having a top surface in contact with the back surface of the spacing layer and a topcoat and/or cover sheet overlying and conforming to the top surfaces of the lenses and having a flat top surface or face. In another embodiment, the retroreflective sheeting includes a pressure sensitive adhesive underlying and in contact with the reflective layer. The retroreflective sheeting has an image whose proportions are determined by a nonconformity of the reflective and spacing layer to the bottom of the lenses. The image of the present invention can range from conspicuous to inconspicuous and directional to non-directional.

CROSS REFERENCE TO PROVISIONAL APPLICATION

This application claims priority from provisional application Ser. No.60/106,359, filed Oct. 30, 1998, the entire disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a retroreflective sheeting with animage, more specifically a validation image.

BACKGROUND OF THE INVENTION

Validation images have been used for years for authentication andsecurity purposes. A watermark is an identifying pattern or legendeither on or in a material to provide validation of the material.Retroreflective sheeting with directional and non-directional watermarkshave been used as a validation means for documents, phonographs,cassette tapes, compact disk containers, traffic signage and licenseplates.

One problem with watermarks on retroreflective material is providing thewatermark in a manner which provides the needed authentication but whichprovides some subtlety or inconspicuousness, such as being discerniblein only a few angles of viewing. Often expensive processing steps andequipment are required to provide such a watermark. Additionally, thereis generally little processing control over the conspicuousness orintensity of the watermark.

It is desirable to have an image which is distinct and viewable forauthenticating purposes. Further, it is desirable to have a processingmeans to provide the desired intensity of the image. Finally, it is alsodesirable to have an image which may be subtle and directional.

SUMMARY OF THE INVENTION

This invention relates to retroreflective sheeting which has an image,such as a validation image. In one embodiment, the image is directionalhaving varying appearance at different angles of view. Theretroreflective sheeting has a layer of transparent microsphere lenses,a transparent polymeric spacing layer underlying, contacting, andconforming to the bottom of the lenses, the spacing and conformation ofwhich is critical to the optimal performance of the retroreflectivearticle, a reflective layer having a top surface in contact with theback surface of the spacing layer and a topcoat and/or cover sheetoverlying and conforming to the top surfaces of the lenses and having aflat top surface or face. In another embodiment, the retroreflectivesheeting includes a pressure sensitive or thermally activated adhesiveunderlying and in contact with the reflective layer. The retroreflectivesheeting has an image whose proportions are determined by anonconformity of the reflective and spacing layer to the bottom of thelenses. The image of the present invention can range from conspicuous toinconspicuous and directional to non-directional.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a retroreflective sheeting.

FIG. 2 is a cross sectional view of a retroreflective sheeting.

FIG. 3 is a cross sectional view of a retroreflective sheeting.

FIG. 4 is an illustration of the method of imparting the image.

FIG. 5 is an illustration of an alternative method of imparting theimage.

FIG. 6 is an illustration of an another alternative method of impartingthe image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described herein, the invention relates to a retroreflective sheetingwhich has an image. The image is a portion of the reflective layer whichdoes not conform, or is less conforming to the back surface of themicrosphere lenses. The portion of the reflective layer, which is out ofconformity, does not provide the same magnitude of retroreflectivity asthe conforming areas. This non-conforming area can range from a “dead”or nonreflecting, to a less reflecting portion, to a greater reflectingportion of the retroreflective sheeting. This difference in reflectivecharacteristic leads to the image's viewability. The apparent intensityof the image is related to the degree of non-conformity of the spacingand/or the reflective layers.

As described above the retroreflective sheeting has a layer oftransparent microsphere lenses. The microsphere lenses may have anyrefractive index or average diameter provided that the beads provide thenecessary refraction for the retroreflective application. Typically themicrosphere lenses are characterized as having an average refractiveindex in the range of about 1.8 to about 2.5, or from about 1.9 to about2.4, or from about 2.1 to about 2.3 and an average diameter of about 35to about 100, or from about 45 to about 90, or from about 55 to about 80microns. Here and elsewhere in the specification and claims the rangeand ratio limits may be combined. The transparent microsphere lensesutilized in the retroreflective sheeting of the present invention may becharacterized as having average diameters in a range of from about 25 toabout 300, 30 to about 120 microns, and more often in a range from about40 to about 80 microns. The index of refraction of the microspherelenses is generally in the range from about 1.9 to about 2.5, moretypically is in the range from about 2.0 to about 2.3, and most oftenbetween about 2.10 to about 2.2.

Glass microspheres are typically used although ceramic microspheres suchas those made by sol/gel techniques can also be used. The index ofrefraction and the average diameter of the microspheres, and the indexof refraction of the topcoat and/or cover sheet and space coat dictatethe thickness of the spacing film. The microspheres can be subjected tochemical or physical treatments to improve the bond of the microspheresto the polymeric films. For example, the microspheres can be treatedwith a fluorocarbon or an adhesion promoting agent such as anaminosilane to improve the bond, or the space coat layer in which thelenses have been embedded can be subjected to a flame treatment orcorona discharge to improve the bond between the space coat and lensesto the subsequently applied topcoat and or cover sheet.

The retroreflective sheeting also has a spacing layer generallyconforming to the bottom surface of the microsphere lenses. Thethickness of the polymeric spacing layer or space coat is from about 25%to about 100%, or from 40% to about 60% of the average diameter of themicrosphere lenses. Various thermoplastic polymeric resins have beenused previously in forming the spacing layer of embedded lensretroreflective sheeting, and such resins can be used in the sheeting ofthe present invention. The resins that may be used for the spacing layerinclude a variety of partially amorphous or semi-crystallinethermoplastic polymers which generally have a soft stage during whichthe lenses can be embedded in the films. The material used to form thespacing film or layer should be compatible with the topcoat material andadapted to form a good bond with the topcoat (and the microspherelenses). Preferably, the adhesion between the materials is greater thanthe tensile strength of the materials. Acrylics, polyvinyl butyrals,aliphatic urethanes and polyesters are particularly useful polymermaterials because of their outdoor stability. Copolymers of ethylene andan acrylic acid or methacrylic acid; vinyls, fluoropolymers,polyethylenes, cellulose acetate butyrate, polycarbonates andpolyacrylates are other examples of polymers that can be used for thetopcoat and spacing layers of the sheeting of the invention. In oneembodiment it is desirable to use materials having elastomericproperties to provide retroreflective sheeting which may be repeatedlystretched or flexed, and upon release of the stretching or flexingtension, rapidly return to substantially their original dimensionswithout significant loss of retroreflectivity. Polyurethanes areavailable which possess such elastomeric properties and these materialscan be used as space coat materials.

In another embodiment it is desirable to use two or more layers to forma topcoat/cover sheet layer. These may consist of any of theaforementioned materials in combination with a transparent pressuresensitive adhesive (such as AS352RX acrylic adhesive from Avery Chemicalin Mill Hall Pa.) underlying the cover sheet and in intimate contact andconforming to the microspheres. The cover sheet or pressure sensitiveadhesive can be colored with a transparent pigment or dye or even beprinted with a graphic which can be located on the interior or theexterior of the cover sheet. In yet another embodiment the pressuresensitive adhesive can be replaced by a thermal bonding layer, a heatactivated adhesive, or a material which forms chemical bonds to thecover sheet.

The retroreflective sheeting has a topcoat or cover sheet overlying andconforming to the top surface of the microsphere lenses. The coatingweight of the topcoat may range from about 25 to 175 gms/m². Preferablythe coating weight is about 50 to 150 gms/m² and more preferably is fromabout 60 to 120 gms/m². The topcoat thickness may range from 25 to about125 microns and more often is from about 50-100 microns.

The cover may comprise various thermoplastic polymers including acrylicpolymer such as polymethylmethacrylate, vinyl polymers such as PVC andvinyl acrylic copolymers, or polyurethanes such as aliphatic polyetherurethanes. Cover sheets include an impact modifiedpolymethylmethacrylate (PMMA) (e.g., Plexiglas™ acrylic DR, MI-7 (Rohm &Haas), Perspex™ acrylic HI-7 (ICI), or blends thereof), a vinyl acrylicformulation (methyl methacrylate/butyl methacrylate) copolymer and a PVChomopolymer) or a polyurethane. The aliphatic polyurethane cover sheetis produced by casting the urethane onto a polymer coated paper castingsheet or onto a polymer casting sheet. Casting sheet products are wellknown to the industry and supplied by companies such as Felix SchoellerTechnical Papers, Pulaski, N.Y., S. D. Warren of Newton Center,Massachusetts and Ivex Corporation of Troy, Ohio. The urethane coatingis coated onto the casting sheet by standard coating methods such ascurtain coating, slot die coating, reverse roll coating, knife over rollcoating, air knife coating, gravure coating, reverse gravure coating,offset gravure coating, Meyer rod coating, etc. To achieve properperformance and coat weight thickness in each of the coating operations,technical expertise is applied to determine the optimal urethanesolution viscosity. The application of these coating techniques is wellknown in the industry and can effectively be implemented by one skilledin the art. The knowledge and expertise of the manufacturing facilityapplying the coating determine the preferred method. Further informationon coating methods can be found in “Modem Coating and DryingTechnology”, by Edward Cohen and Edgar Gutoff, VCH Publishers, Inc.,1992. Extrusion or extrusion coating are alternate methods of forming aurethane film.

The retroreflective sheeting may also include a pressure sensitiveadhesive and optionally a release liner. For example, an adhesive layercan be applied over the reflective layer to protect the reflective layerand to serve a functional purpose such as adhering the sheeting to asubstrate. Conventional pressure-sensitive adhesives such asacrylic-based adhesives, or heat- or solvent-activated adhesives aretypically used and may be applied by conventional procedures. Forexample, a preformed layer of adhesive on a carrier web or release linercan be laminated to the reflective layer. Conventional release linerscan be utilized in the formation of the retroreflective sheeting of thepresent invention.

The retroreflective sheeting is further illustrated in reference to thedrawings. In FIG. 1, retroreflective sheeting 10 has a cover sheet, e.g.a polyurethane 11, in which are embedded glass microspheres 12. Theglass microspheres are also adhered to spacecoat, e.g. polyvinylbutyral,13. Reflecting surface (vapor deposited aluminum) 14 is attached tospacecoat 13. A pressure sensitive adhesive 15 and release liner 16 areadhered to reflecting surface 14. Images 17 and 18 are portions of thereflective and spacecoat layers which are non-conforming to the glassbeads 12.

FIG. 2 illustrates a retroreflective sheeting which does not have apressure sensitive adhesive. Retroreflective sheeting 20 has cover sheet21 attached to glass microspheres 22, which are also attached tospacecoat 23. A reflecting surface 24 is on spacecoat 23. Images 25 and26 are non-conforming sections of the reflective and spacecoat layers 23and 24.

FIG. 3 illustrates a retroreflective sheeting which has a multilayercovering. Retroreflective sheet 30 which has cover sheet 31 which isadhered to pressure sensitive adhesive 32. Adhesive 32 is bonded toglass microspheres 33, which are also attached to spacecoat 34. Areflecting surface 35 is on spacecoat 34. The reflecting surface 35 isadhered to pressure sensitive adhesive 36 which is also releasablyadhered to release liner 37. The retroreflective sheeting has images 38and 39.

The images of the present invention may be prepared by using embossingor flexographic printing techniques. The images may be prepared bypressing a pattern into the retroreflective sheeting at the pressure andtemperature necessary to provide the desired image.

The retroreflective sheeting can be made by procedures normally used inthe industry. For example, the sheeting of the invention can be preparedby first extruding or casting a space coat layer of desired thickness ona polymer coated casting sheet and drying if necessary. The space coatlayer is reheated to provide a tacky surface upon which microspheres arecascade-coated to form a monolayer of the microspheres. Typically, heatand/or pressure can be applied at this stage to facilitate microsphereembedding. The microspheres generally are embedded into the layer to adepth of about one-half of the average diameter of the microspheres. Itis important that the space coat adapts a contour parallel to themicrosphere surface. The topcoat is then applied over the top of theexposed and partially embedded microspheres.

The topcoating is applied by standard coating methods such as thosedescribed above. It is also possible to cast the topcoat as a separate,single layer film using these coating techniques. To achieve properperformance and coat weight thickness in each of the coating operations,technical expertise must be applied to determine the optimal solutionviscosity. The application of these coating techniques is well known andis described above. Extrusion or extrusion coating are alternate methodsof forming a topcoat. If required, the topcoat and the base coat layerare then subjected to an elevated temperature to dry or cure.

The polymer coated casting sheet then is stripped from the space coatlayer, and a reflective layer is subsequently applied over the backsurface of the space coat. For example, a reflective layer of silver oraluminum metal can be applied by vapor deposition over the back surfaceof the space coat. The thickness of the reflective layer depends on theparticular metal used and is generally between about 500 and 1000nanometers. The topcoat layer then can be printed (e.g. with UVradiation curable inks) to provide monocolor or multicolor images withthe optional transparent overcoat.

An alternate manufacturing process for enclosed bead-typeretroreflective products can be used by first applying a polyurethanemixture onto a casting sheet and exposing the newly cast film to heatfor solvent evaporation and urethane curing. After the film is formed, abead bonding layer is applied and typically exposed to elevatedtemperatures for curing and/or evaporation of a carrier vehicle, such assolvent. Though many materials may be used for the bead bond layer, athermoplastic polymer is preferred. The bead bond layer can then bepartially cured or re-softened by the application of heat to allowcascade coated microspheres to form a monolayer of microspheres. Themicrospheres generally are embedded into the bead bond layer in aprocess that uses the application of heat and/or pressure. The spacecoat layer of desired thickness is then applied over the exposedmicrospheres. Next, the space coat and base coat layers are subjected toelevated temperatures to complete solvent drying and/or curing and toprovide adequate conformation of the spacecoat to the microspheresurface.

As described above, a reflective layer is subsequently applied over theback surface of the space coat layer. After the original casting sheetis stripped from the product, the top aliphatic polyurethane layer canbe printed (e.g. with UV radiation curable inks) to provide monocolor ormulticolor images with the optional transparent overcoat or overlaminatefilm.

In another embodiment, the retroreflective sheeting described in aprevious paragraph is provided with a pressure-sensitive adhesiveconstruction. In this embodiment, a pressure-sensitive adhesive iscoated onto a release coated liner (paper or polymer) thereafter theadhesive coated liner is pressure laminated to the exposed surface ofthe reflective layer. This embodiment is illustrated in FIG. 1. Therelease coated liner can subsequently be removed and the retroreflectivesheeting can be adhesively applied to other surfaces.

The validation image has at least one portion which is non-conforming tothe lenses. In one embodiment, the image is prepared by pressing theimage design into the reflective surface of the retroreflectivesheeting. The reflective layer of retroreflective sheeting is forcedagainst a heated roll, such as a heated steel roll, by another roll,such as a rubber embossing or a flexo printing roll, containing thedesign of the image. The pressure and temperature as well as the speedof the roll affect the flattening of the crowns of the reflective layer.The pressure is typically from about 5 to about 75, or from about 10 toabout 35, or from about 15 to about 25 pounds per linear inch (pli). Thetemperature of the heated roll is from about 85 to about 130, or fromabout 90 to about 120, or from about 95 to about 110 degrees C. Thespeed of the roll is typically from about 5 to about 100, or from about8 to about 80, or from about 10 to about 60 ft/min. In one embodiment,the mechanical stops on the embossing and flexographic printingequipment are set to control the depth of the impression of the image.The mechanical stops are set so that the roll with the image design isnot forced onto the heated roll when between the raised image designs.The roll with the image design then just touches or kisses the surfaceof the retroreflective sheeting, thus forming the image.

FIG. 4 illustrates the method of imparting the image. Heated steel roll41 contacts the reflective side of retroreflective sheeting 42. Thetopcoat side of sheeting 42 is pressed against flexographic roll 43bearing the raised impression 44 of the desired image. After beingsubjected to the heating and pressing step, the sheeting 42 has images.

The roll used for the image design may be any roll used for embossing orflexo printing. The advantage of the present process is that therelatively inexpensive equipment may be used for preparing theretroreflective sheeting with the image. With the use of the heated rollthe present process provides a simple means to prepare a retroreflectivesheeting with an image.

An alternative method of imparting an image can be made by firstembossing an image into the face of the polymer coated surface of acasting sheet. This can easily be done into thermoplastic materialsusing the techniques for embossing holographic images. For example, thesheeting of the invention can be prepared by first extruding or castinga space coat layer of desired thickness on an imaged polymer coatedcasting sheet and drying if necessary. The space coat layer is reheatedto provide a tacky surface upon which microspheres are cascade-coated toform a monolayer of the microspheres. Typically, heat and/or pressurecan be applied at this stage to facilitate microsphere embedding. Themicrospheres generally are embedded into the layer to a depth of aboutone-half of the average diameter of the microspheres. It is importantthat the space coat adapts a contour parallel to the microsphere surfaceand that the image substantially remains intact. The topcoat is thenapplied over the top of the exposed and partially embedded microspheres.

The topcoating is applied by standard coating methods as describedabove. Extrusion can be considered as an alternate method of forming atopcoat if required, the topcoat is then subjected to an elevatedtemperature to dry and/or cure the mixture.

The polymer coated casting sheet then is stripped from the imaged spacecoat layer, and a reflective layer is subsequently applied over the backsurface of the space coat as described above. The topcoat layer then canbe printed as described above.

FIG. 5 illustrates an alternative method of imparting the image. In FIG.5a, article 50 has a substrate 51 which is adhered to polymer film (e.g.polyethylene) 52. Heat and pressure are used to emboss an image 53, suchas a holographic image into the surface of a polymer film 52. In FIG.5b, spacecoat (e.g. polyvinylbutyral) 54 is coated on to polymer film52. The image 53 in polymer 52 is replicated in the bottom surface ofspacecoat 54. In FIG. 5c, glass microspheres 55 are embedded intospacecoat 54, the spacecoat is molded by the polymer layer 52 to acontour parallel to the microsphere surface and the image substantiallyremains intact. In FIG. 5d, a topcoat 56 is coated on the exposedsurface of the glass microspheres 55. In FIG. 5e, the substrate 51 andpolymer film 52 are removed from the construction. The spacecoat 54 withholographic images 53 is metallized as described above to form areflective layer 57.

Another alternative method of imparting an image can be made by firstprinting an image using a transparent polymer or a transparently coloredpolymer onto the face of the polymer coated surface of a casting sheet.The printing can be done using common printing techniques such asFlexography (flexo) and Rotogravure (gravure). Heat and pressure areused to press the image into the face of the polymer coated substrate sothat the top of the print is substantially level with the polymer coatedsurface. For example, the sheeting of the invention can be prepared byfirst extruding or casting a space coat layer of desired thickness on animaged polymer coated casting sheet and drying if necessary. The spacecoat layer is reheated to provide a tacky surface upon whichmicrospheres are cascade-coated to form a monolayer of the microspheres.Typically, heat and/or pressure can be applied at this stage tofacilitate microsphere embedding. The microspheres generally areembedded into the layer to a depth of about one-half of the averagediameter of the microspheres. It is important that the space coat adaptsa contour parallel to the microsphere surface and that the imagesubstantially remains intact. The topcoat is then applied over the topof the exposed and partially embedded microspheres.

The topcoating is applied by standard coating methods as describedabove. Extrusion can be considered as an alternate method of forming atopcoat. If required, the topcoat and the base coat layer are thensubjected to an elevated temperature to dry or cure.

The polymer coated casting sheet then is stripped from the imaged spacecoat layer, and a reflective layer is subsequently applied over the backsurface of the space coat as described above. The printed image isnon-conforming with the microspheres. The topcoat layer then can beprinted (e.g. with UV radiation curable inks) to provide monocolor ormulticolor images.

FIG. 6 illustrates an alternative method of imparting the image. In FIG.6a, article 60 has a substrate (e.g. paper) 61 which is adhered topolymer film (e.g. polyethylene) 62. An image is printed using atransparent or transparently colored polymer (e.g. polyvinylbutyral) onthe surface of polymer 62. In FIG. 6b, the image 63 is embedded intopolymer layer 62 using heat and pressure. In FIG. 6c, spacecoat (e.g.polyvinylbutyral) 64 is coated onto the surface of polymer film 62containing embedded images 63. In FIG. 6d, glass microspheres 65 areembedded into spacecoat 64, the spacecoat is molded by the polymer layer62 to a contour parallel to the microsphere surface and the imagesubstantially remains intact. In FIG. 6e, a topcoat (e.g. aliphaticpolyurethane) 66 is coated on the exposed surface of the glassmicrospheres 65. In FIG. 6f, the substrate 61 and polymer film 62 areremoved from the construction. The spacecoat 64 with images 63 ismetallized as described above to form a reflective layer 67.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

What is claimed is:
 1. A retroreflective sheet with an image comprisinga layer of transparent microsphere lenses, a transparent polymericspacing layer contacting and conforming to the bottom of the lenseswherein the spacing layer has at least one portion which isnon-conforming to the lenses, a reflective layer having a top surface incontact with the back surface of the spacing layer and a topcoat and/orcover sheet overlying and conforming to the top surfaces of the lensesand having a flat top surface or face wherein the non-conforming portionof the spacing layer forms the image.
 2. The retroreflective sheet ofclaim 1 wherein the microspheres have an average refractive index in therange of about 1.8 to about 2.5.
 3. The retroreflective sheeting ofclaim 1 wherein the microspheres are glass microspheres with a averagediameters in a range of from about 25 to about 300 microns.
 4. Theretroreflective sheet of claim 1 wherein the spacing layer is an acrylicpolymer, a polyvinyl butyral, an aliphatic urethane and a polyester. 5.The retroreflective sheet of claim 1 wherein the spacing layer ispolyvinylbutyral.
 6. The retroreflective sheet of claim 1 wherein thethickness of the polymeric spacing layer is from about 25% to about 100%the average diameter of the microsphere lenses.
 7. The retroreflectivesheet of claim 1 wherein the topcoat has a thickness from about 25microns to about 300 microns.
 8. The retroreflective sheet of claim 1wherein the topcoat is derived from at least one acrylic polymer, avinyl polymer, or polyurethanes.
 9. The retroreflective sheet of claim 1wherein the sheet includes a topcoat and a cover sheet.
 10. Theretroreflective sheet of claim 9 wherein the topcoat is a pressuresensitive adhesive and the cover sheet is derived from at least oneacrylic polymer, a vinyl polymer, or polyurethanes.
 11. Theretroreflective sheet of claim 9 wherein the topcoat is a partiallycured urethane and the cover sheet is derived from at least one acrylicpolymer, a vinyl polymer, or polyurethanes.
 12. The retroreflectivesheet of claim 9 wherein the topcoat is a heat activated adhesive andthe cover sheet is derived from at least one acrylic polymer, a vinylpolymer, or polyurethanes.
 13. The retroreflective sheet of claim 1further comprising a pressure sensitive adhesive underlying and incontact with the reflective layer.
 14. A retroreflective sheet with animage comprising a monolayer of transparent glass microsphere lenses, apolyvinylbutyral transparent polymeric spacing layer contacting andconforming to the bottom of the lenses, a reflective layer having a topsurface in contact with the back surface of the spacing layer and apolyurethane topcoat and/or cover sheet overlying and conforming to thetop surfaces of the lenses and having a flat top surface or face whereinthe image is a non-conforming portion of the spacing layer and thereflective layer.
 15. The retroreflective sheet of claim 14 wherein themicrospheres have an average refractive index in the range of about 2.0to about 2.3.
 16. The retroreflective sheeting of claim 14 wherein themicrospheres are glass microspheres with a average diameters in a rangeof from about 30 to about 120 microns.
 17. The retroreflective sheet ofclaim 14 wherein the coating thickness of the polymeric spacing layer orspace coat is from about 35% to about 75% of the average diameter of themicrosphere lenses.
 18. The retroreflective sheet of claim 14 whereinthe topcoat has a thickness from about 25 microns to about 125 microns.19. The retroreflective sheet of claim 14 further comprising a pressuresensitive adhesive underlying and in contact with the reflective layer.